This application relates to a temporary coating for a sealed compressor, to provide lubricant at bearing surfaces for start-up.
Refrigerant compressors are typically mounted in a sealed container. An electric motor is provided in the sealed container and drives a rotating shaft. The rotating shaft drives a pump unit to compress the refrigerant.
One known type of compressor pump unit is a scroll compressor. In a scroll compressor, the rotating shaft has an eccentric pin that works in combination with a rotation prevention mechanism, typically an Oldham coupling, to cause orbiting movement of an orbiting scroll member. The orbiting scroll member has a base with a generally spiral wrap extending from the base. The wrap interfits with a wrap from a non-orbiting scroll member, and compression chambers are defined between the two wraps. As the orbiting scroll member orbits, the size of the compression chambers decreases and an entrapped refrigerant is compressed.
In scroll compressors, and in other types of compressors, a liquid lubricant is typically pulled upwardly through passages in the shaft to lubricate sliding surfaces in the compressor pump unit. The lubricant serves to lubricate the surfaces, and prevent wear or other damage to the components sliding or rotating relative to each other.
However, at start-up, it may be the case that sufficient liquid lubricant will not be at those surfaces. Thus, there may sometimes be damage to the surfaces before the lubricant can reach the sliding surfaces. This is especially true at initial run-in of the compressor, when it is initially started.
In particular, at initial run-in of the compressor, a problem called “edge loading” can occur, since there is typically some small misalignment between the rotating shaft and several bearings that mount the shaft. This misalignment can result in edges of the bearing contacting the shaft over a limited surface, rather than providing support over a larger surface area. Seizure and undue wear of portions of the components can occur, which is undesirable. This problem is made more acute if there is insufficient lubricant during the initial run-in.
Also, modern refrigerants, which may include mixtures of R32 and R125, or a mixture of R143a and R125 can have some undesirable interaction in compressors utilizing ester oil or ether oil as a lubricant. In such compressors, the refrigerant which circulates over the bearing surfaces, can pull the lubricant away from the bearing surfaces back downwardly into the sump. When this occurs, there is even less lubricant during the initial start-up.
It is known in the prior art to provide various types of bearings having self-lubricating properties. As an example, any number of prior art patents have proposed utilizing bearings having impregnated polytetrafluoroethylene (“PTFE”) material. In general, these proposals could be characterized as somewhat complex and expensive.
In addition, these bearings do not address the lack of liquid lubricant at the sliding surfaces at initial start-up of the compressor.